For example, U.S. Pat. No. 5,901,363 discloses a technique concerning a group call. That is, first, a subscriber (A, B, C, D) belonging to a group call group and wishing to speak requests a speech item to a mobile exchanger through an interface. In order to solve problems caused by concurrent requests for a speech transmission turn from two subscribers, when the request for the speech item from the subscriber (A, B, C, D) is detected, priority data (B′, C′) specific to the request for the speech item and including the priority is generated, and the mobile exchanger switches the speech signal transmitted by that subscriber whose request for the speech item has priority data (B′) of the highest priority for the other subscribers to hear.
According to such a background art as described above, although the transfer of the right to speak can be controlled, consideration is not given to the transfer of the right to speak in view of such usability that for example, a specific person who is expected to speak is made to have the right to speak, and/or the right to speak is controlled so as to avoid such a state that a specific speaker continues to have the right to speak and other group members cannot acquire the right to speak.